Photographic developer replenishment

ABSTRACT

DEVELOPER REPLENISHER IS ADDED TO A BATH OF PHOTOGRAPHIC DEVELOPER, IN ACCORDANCE WITH MONITORING OF A TEST STRIP OF PHOTOGRAPHIC MATERIAL DEVELOPER BY DEVELOPER SAMPLED FROM THE BATH, FOR THE PURPOSE OF COMPENSATING FOR ANY LOSS IN ACTIVITY THAT OTHERWISE WOULD OCCUR BECAUSE OF USE, AGING, OR OTHER REASON. THE PHOTOSENSITIVE TEST STRIP IS TRANSPORTED SUCCESSIVELY THROUGH AN EXPOSURE CHAMBER WHEREIN IT IS EXPOSED TO ACTINIC LIGHT, A DEVELOPMENT CHAMBER WHEREIN THE EXPOSED STRIP IS DEVELOPED BY THE SAMPLE OF DEVELOPER, AND FINALLY A MONITORING CHAMBER WHEREIN THE DEVELOPED OPTICAL DENSITY OF THE STRIP DETERMINES THE AMOUNT OF LIGHT PASSING FROM A NON-ACTINIC LIGHT SOURCE TO A PHOTORESISTIVE ELEMENT IN AN ELECTRONIC SYSTEM FOR CONTROLLING THE ADDITION OF REPLENISHER TO THE DEVELOPER BATH. THE MONITORED DENSITY IS CHECKED CONTINUOUSLY AGAINST A VALUE CORRESPONDING TO AN ACCEPTABLE PLATEAU OF DEVELOPER ACTIVITY, AND ALSO PERIODICALLY FOR ANY DECREASE IN DENSITY AS COMPARED WITH THE RESULTS OBTAINED WHEN LAST PREVIOUSLY CHECKED, AND IF DEFICIENT IS ADJUSTED UPWARD BY INTERMITTENT ADDITION OF REPLENISHER IN ACCORDANCE WITH THE PREVAILING RATE OF DECREASE IN DENSITY.

Nov. 30, 1971 C. s. OST

PHOTOGRAPHIC DEVELOPER REPLENISHMENT 3 Sheets-Sheet 1 Filed Aug, 11, 1969 /w 7 r), f 5 wn C .4.. f we Mc H Y C8 Nov. 30, 1971 c. s. OST 3,623,418

PHOTOGRAPHIC DEVELOPER REPLENISHMENI Filed Aug. 11, 1959 l 3 sheets-sheet 2 NOV. 30, 1971 Q 5 OST PHOTOGRAPHI C DEVELOPER REPLENI SHMEN'I 3 Sheets-Sheet 5 Filed Aug. ll, 1969 LL i RL/ me nel United States Patent O 3,623,418 PHOTOGRAPHIC DEVELOPER REPLENISHMENT Clarence S. st, 118 N. Mansfield Ave., Margate City, NJ. 08402 Filed Aug. 11, 1969, Ser. No. 848,867 Int. Cl. G03d 3/12 U.S. Cl. 95--89 R 14 Claims ABSTRACT OF THE DISCLOSURE Developer replenisher is added to a bath of photographic developer, in accordance with monitoring of a test strip of photographic material developed by developer sampled from the bath, for the purpose of compensating for any loss in activity that otherwise would occur because of use, aging, or other reason. The photosensitive test strip is transported successively through an exposure chamber wherein it is exposed to actinic light, a development chamber wherein the exposed strip is developed by the sample of developer, and finally a monitoring chamber wherein the developed optical density of the strip determines the amount of light passing from a non-actinic light source to a photoresistive element in an electronic system for controlling the addition of replenisher to the developer bath. The monitored density is checked continuously against a value corresponding to an acceptable plateau of developer activity, and also periodically for any decrease in density as compared with the results obtained when last previously checked, and if deficient is adjusted upward by intermittent addition of replenisher in accordance with the prevailing rate of decrease in density.

This invention relates to replenishment of photographic developer to maintain the activity thereof, as in a bath of developer wherein development is taking place and is thereby depleting the activity of the developer.

Various methods are lknown whereby developer replenisher is added to a bath of photographic developer, with the object of maintaining its activity. Howe-ver, such methods either are based upon inaccurate assumptions, such as constant time-rate of loss in activity despite variations in average degree of exposure or quantity of material being processed per unit of time or upon imperfect techniques of sampling or evaluation of the developer.

A primary object of the present invention is improved sampling of photographic developer for monitoring of the activity thereof.

Another object is improved monitoring of the activity of sampled photographic developer for determination of changes therein and of the desirability of adding developer replenisher.

A further object is improved addition of developer replenisher to photographic developer in accordance with monitoring of developer activity and changes therein.

Yet another object is provision of apparatus for performing the foregoing process steps automatically.

Still further objects of this invention, together with means and methods for attaining the various objects, will be apparent from the following description and the accompanying diagrams.

FIG. 1 is a view in side elevation, partly schematic, of apparatus components of this invention, especially in relation to a test strip of photographic material;

FIG. 2 is a like View of another embodiment of components relative to a test strip;

FIG. 3 is a view in enlarged side sectional elevation of one of the apparatus components of the preceding iviews, specifically a block comprising an exposure chamber;

FIG. 4 is a perspective view of components of the apparatus of FIG. 3;

FIG. 5 is a plan view of lm exposed in the apparatus of the immediately preceding views;

FI-G. 6 is a like view of film exposed in somewhat modied manner;

FIG. 7 is a view in enlarged side sectional elevation of another component of FIGS. l and 2, specifically a block comprising a development chamber and a monitoring chamber;

FIG. 8 is a largely diagrammatic view of developercontaining means and related items', and

FIG. 9 is a schematic showing of electrical apparatus useful according to the invention.

In general, the -objects of the present invention are accomplished by exposing a test strip of photographic material, extracting from a bath of developer in which subject photographic material is being developed a sample of such developer, developing the exposed test strip with the sample of developer, sensing optical density of the developed strip, and adding developer replenisher from a source thereof to the developer bath in accordance therewith.

FIG. 1 shows test strip 10 of photographic material stored in unexposed form on supply reel 11 shown fragmentarily at the left, from which it unwinds over roller 12, between exposure block 13 and pressure pad 14, then between development and monitoring block 23 and pressure pad 24, through the nip of drive roll 27 and idler roll 28, and onto takeup roll 31 shown fragmentarily at the right. The respective pressure pads are resiliently supported on leaf springs 15 and 25, the opposite end thereof being secured by respective brackets 15a and 25a to a supporting frame (indicated only diagrammatically). Idler roll 28 is pivotally supported on swing arm 26, the other end of which is pinned to the frame, and is biased toward drive roll 28 by extension spring 29 attached to an intermediate part of the arm. The drive roll is rotated by synchronous strip transport motor 30 to forward the test strip onto takeup reel 31. Electrical power is supplied by a pair of leads from external connection points x, y to the motor, to the exposure block via constamt-voltage device 9 and to the development and monitoring block via constant-voltage device 19. The latter block has respective developer sample inlet and outlet tubes 33 and 34 extending from its base, and its pressure pad 24 has pair of electrical leads 37 and 38 extending therefrom to ground and to external point a, respectively. The functioning of the items illustrated in FIG. 1 is considered in detail hereinafter.

FIG. 2 contains essentially everything shown in FIG. l plus certain additional items interposed between exposure block 13 and development and monitoring block 23. Added synchronous strip transport motor 50 rotates drive roll 47, toward which idler roll 48 on swing arm 46 is biased by extension spring 49 to form a nip to receive and forward test strip 10 of photographic material. The test strip then passes under idler roll 52 carried on swing arm 56, which is biased by extension spring 59 away from a straight-line path, and over idler roll 58 mounted on a fixed axis in the straight-line path. Also attached to swing arm 56 is actuating arm 61 of limit switch 62, which has switch arm 63 in one side of the power line such that the switch is opened when there is enough Slack in the test strip to permit an extreme downward swing of the arm and such that the switch is closed when there is such a minimum of slack in the test strip to raise the arm to an extreme upward position. Synchronous strip transport motor 30 in the vicinity of takeup reel 31 is not connected to the external power line connections in this embodiment but is connected to points 1', i identified further hereinafter.

FIG. 3 shows, exposure block 13 enlarged and sectioned to reveal the interior chamber, which is in the form of a cylindrical bore with lamp 16 in the lower end thereof and with umbra-penumbra slits 17, 18 intervening between the lamp and the overlying test strip, as shown further (in perspective) without the exposure block itself in FIG. 4. Pressure pad 14 is shown in phantom in its alternative lifted position (with leaf spring 15 flexed) which facilitates introduction of the test strip to cover the open upper end of the chamber bore.

FIGS. and 6 show developed test strip portions 10 and respectively, with developed variable-density characteristics corresponding to varying exposures along the strip length. The variable-width clear track flanked by an opaque background, as shown in FIG. 5, results from application of a hard (high contrast) litho type of developer to a strip exposed with the slit geometry of FIGS. 3 and 4. A homogeneous varying density characteristic, as shown in FIG. 6, will result from exposure through a single plain slit similar to 17 located close to the lamp, upon development with a soft (low contrast) developer. IEither of the above or other techniques may be used satisfactorily in the practice of this invention.

FIG. 7 shows development and monitoring block 23 enlarged and sectioned to show the interior chambers formed by left and right vertical bores 71 and 81 therethrough and overlain by pressure pad 24, which is also shown (in phantom) in its alternative lifted position with supporting leaf spring 25 ilexed accordingly. Left bore 71 receives sample inlet tube '33 and sample outlet tube 34 in watertight contact at its bottom end. The inlet tube terminates in communication with the bore at that end, but the outlet tube continues upward toward the top end and terminates in communication with central opening 73 in spacer 70, which defines development space 74 at the top of the bore. At its left and right edges the spacer has pair of gaps 72, through which developer passes into the development space, from which it exits through the central opening in the spacer, as indicated by arrows.

The monitoring chamber through which the test strip passes next is composed of bore 81 in block 23 and bore 82 in pressure pad 24. Lamp 83 removably retained by seat 87 in the upper part of bore 81 has electrical leads extending thereform and out the bottom of the block to constant-voltage device 19. Filter 85 in the top end of bore 81, between lamp 83 and test strip 10 (now developed and coated with developer) renders the light transmitted thereby non-actinic to avoid further exposure (and development) of the test strip. Located in overlying bore 82 and juxtaposed to the opposite side of the `test strip from lamp '83 is densitometer head 84, whose electrical photoresistance (R4, not separately shown) varies in accordance with the intensity of light incident 'thereon as transmitted through the developed test strip and whose electrical leads connect to ground and to point a, respectively, as shown in FIGS. 1 and 2.

FIG. 8 shows bath 92 of developer in developing tank 91, in which subject photographic material supported by belt 90 is being developed as it is transported about sets of rollers, including drive roller 93. Pipe `94 leads from lthe bottom of the tank past a junction with `tube 34, which is the sample outlet tube from the test development charnber in monitoring block 13. Pump P is present in the pipe between that junction and a junction with tube 33, which is the sample inlet tube to the test development chamber, to produce the desired circulation (indicated by arrows). Before discharging into the top of development tank `91, pipe `94 is constricted into venturi `95, to which replenisher tube 96 is connected. The other end of tube 96 is immersed in supply of developer replenisher 97 in container `98. Between its ends the tube is enlarged into flow chamber 99. The interior of the flow chamber is so constructed that opening of valve 103 electrically by solenoid 104 will enable replenisher to flow, at a rate indicated by flowmeter 100 and controllable by manual setting of knob 102 to series valve 101, from container 98 through tube 96 and into pipe 94 to tank 91, where it mixes with bath 92 developer therein to raise the activity thereof. The pump is driven by motor M connected to external power points x, y and provided with manually actuatable speed-control means having control dial 105. As indicated by interconnecting broken lines, motor M also turns drive roll y93, so as to transport subject photographic material supported by belt through developer bath `92, and rotates electrical alternator G, which connects to points i, i also shown in FIG. 2 as connecting to the leads for synchronous strip transport motor 30 for which the alternator furnishes electrical power in that embodiment. The solenoid coil connects to external power point y and to control point c, which is identified further in the description of the next View.

FIG. 9 shows electrical control apparatus of this invention, largely schematically and partly in block form. Control point c, previously shown in FIG. 8, is at the right alongside external power point x. At the left of the view is comparison means including a resistance bridge. The bridge is composed of fixed resistors R1 and R3 in the upper left and right arms, respectively, adjustable resistor R2 in the lower left arm, and photo-variable resistance R4 (not shown) of dcnsitometer head 84 in the lower right arm as indicated by the lead to point a (also shown in FIGS. 1 and 2). Electrical potential is supplied across the bridge from bottom (positive) to top (negative) by battery B1, and activity meter AM is connected transversely across the bridge as an indicator of bridge balance when centered.

Shown in block form at the lower right of FIG. 9` are trigger circuits 1 and 2, both of which are wholly conventional and, therefore, not further illustrated or described except for input and output elements thereof. These circuits have respective input transistors, T1 and T2. The base of transistor T 2 at the right is connected to receive the bridge output from a terminal at the left side of the bridge (slider of R2). Each such circuit also has an output relay: RL1 for trigger circuit 1, and RLZ for trigger circuit 2. Relay RL1 actuates double-throw switch S1, which has arms A1, A2, and A3, and relay RLZ actuates single-throw switch S2, which has only arm A. Both switches are shown with their arms in the normal rest position occupied thereby 4when not actuated by the relays.

The respective switch arms connect as follows: A1 to capacitor C1, which in turn connects to the left or output side of the bridge; A2 to C2, the other side of which is grounded, and to R6, which goes to the negative terminal of battery B2, the positive terminal of which is grounded; A3 to connection point c (see also FIG. 8); and A to external power point x. The contacts that are closed in the indicated rest position of the switch arms are themselves connected as follows: A1 to one side of diode D, the other side of which is grounded; A2 to the normally closed contact for arm A2 and to resistor R5; which connects to the base of transistor T1; A3 (and A) no contact. The normally open contacts for the respective arms are themselves connected as follows: A1 to the normally colsed contact for arm A2 and to resistor R5; A2 to the positive terminal of battery B3, the negative terminal of which is grounded; A3 and A to one another.

Operation of this invention is readily understood. Test strip 10 of photographic material is unwound from supply reel 11 and is transported, whether according to the FIG. 1 embodiment or the FIG. 2 embodiment (which are distinguished subsequently hereinafter) past exposure block 13 and there exposed bylamp 16, then past test development chamber 71 of development and monitoring block 23, where it is ooded With developer sampled from bath 92 thereof (in tank 91) in `which subject photographic material is being developed. The developed test strip passes between lamp 83 and densitometer head 84, which senses the intensity of light transmitted through the strip as an index of the optical density thereof, before being wound up onto takeup reel 31. The sampling of developer for development of the test strip is continuous, with return of the continual ow of samples back from test development chamber 71 into bath 92.

If the test strip is developed to a sufficient density, the electrical resistance (R4) of the densitometer head 84 will be so high (because of diminution in transmitted light) that the bridge will be in balance or be slightly unbalanced to the right, and will be so shown on activity meter AM, indicating adequate activity. In that event, the output potential at the lead from the left side of the bridge to the base of input transistor T2 of trigger circuit 2 is either positive, zero, or insufliciently negative to cause transistor T2 to conduct and actuate relay RL2, and such closed gate condition precludes addition of developer replenisher, as will become further apparent from the description below.

If the developed test strip is insufficiently dense, transmission of more light therethrough will reduce the densitometer photoresistance R4 suiciently to unbalance the bridge to the left, whereupon the resulting negative polarity causes transistor T2 to conduct, thereby actuating relay RL2, and throwing its arm to the left. If switch S1 is thrown by relay RL1 while trigger circuit 2 is in such open gate condition, the circuit from external power point x to solenoid 104 is completed as both arm A3 of switch S1 and arm A of switch S2 are in their normally open positions. As the other side of the solenoid is always connected to external power point y, the solenold 1s actuated thereby to open valve 103 and thereby cause addition of developer replenisher to the developer circulating into the bath thereof.

Thus, can be seen that the amount of replenisher added depends upon the period during which both relays RL1 and RLZ are closed. As previously mentioned, if the bridge output to the base of transistor T2 goes positive, indicating that a preselected activity plateau has been reached, transistor T2 will cease conducting and relay RLZ will drop out, thereby interrupting the power to the valve solenoid and discontinuing addition of replenisher regardless of conduction by transistor T1. However, so long as the sensed developer activity is less than such -plateau value, replenisher addition will be simultaneous with conduction in transistor T1.

Switch S1 is thrown periodically by relay RL1 whenever the base of transistor T1 becomes negative so that the transistor conducts. The switching repetition rate 1s largely controlled by the time constant of capacitor C2 and resistor R6. Thus, every time switch S1 is thrown, arm A2 connects capacitor C2 directly across battery B3, which charges its upper plate positive. Then, when the relay drops out, arm A2 disconnects capacitor `C2 therefrom and connects it through resistor R6 across battery B2, which has opposite polarity, and the positive charge leaks off the capacitor until the base of transistor T1 becomes slightly negative again, whereupon the cycle repeats.

When switch S1 is thrown by the response of relay RL1 to conduction in transistor T1, and capacitor C2 is removed from the transistor base lead by movement of arm A2 from the normally closed to the normally open position, arm A1 substitutes capacitor C1 in the base lead circuit. Capacitor C1 is in series with the bridge output lead at the left side thereof, and if the sum of the potentials so provided is negative then transistor T1 will conduct until the charge on capacitor C1 leaks off sufficiently by ilow of T1 base current to reach essentially zero total potential, whereupon conduction will cease all down the line and halt the addition of replenisher. It will be noted that the total potential becomes essentially zero and cannot be positive because when switch S1 is in the normally closed position capacitor C1 is connected directly to diode D, which effectively short circuits the capacitor to ground in the instance of such polarity but not otherwise.

The residual potential on capacitor C1 when the net zero potential is reached is retained when switch S1 returns to its normal rest position because the connection from that capacitor to the base lead of transistor T1 is broken thereby and is only replaced by connection to diode D. Thus, if the output becomes more negative during the non-conducting period of the transistor, a negative total potential will result and conduction will occur. It is apparent that the conducting period of the transistor will be substantially proportional to the magnitude of total negaive potential, and essentially so if (as is convenient) resistor R5 is replaced by a constant-current device. However, if the output should become less negative than at the last period the total will be essentially zero and no conduction will occur.

Inasmuch as the only variable in the bridge circuit is the photoresistance R4 of densitometer 84, which increases when it receives less light through the test strip and decreases when it receives more light through the test strip, the net change in the bridge C1 output over one switching repetition period is proportional to the average rate of change of density in the developed test strip and, thus, to the average rate of change of sampled developer activity. The addition period (and, thus, total) of replenisher added at any sample period is likewise proportional to the rate of change in developer activity, rather than to amount of change in activity. Accordingly, whenever the rate of depletion in developer activity increases (or decreases), the control system of this invention responds promptly thereto with'the net result of compensating therefor.

It should be understood that manual ow control valve 101 is set so that the ilow occurring when solenoid 104 opens valve 103 is somewhat higher than would produce a total flow of replenisher exactly suiiicient to compensate for the actual decrease in activity level since the last previous sampling. This is highly desirable, in large part because of time lag inherent in developer circulation and the test development period. The net effect of practicing the process of the invention is to prevent wide swings in developer activity by sensing depletion in activity promptly and proportioning addition of replenisher in accordance with the rate of depletion and, on the other hand, eliminating such addition whenever the sensed activity reaches a preselected activity plateau.

The test strip may be transported according to either the relatively simple arrangement shown in FIG. l or the somewhat more complex system shown in FIG. 2, whichever better meets the needs of the user. Of course, in either event it will be understood that the entire path of the test strip, a least unil it is ready to be wound onto takeup reel 31, is shielded from external light so as to avoid interfering with the testing steps of the process. In the sample procedure of FIG. l, test strip 10 is transported at essentially constant speed through development chamber 71 (as well as the previous exposure chamber and subsequent densitometric chamber) so that its period of development bears no particular relationship to the period of development of subject photographic material supported by belt 90, which normally is a function of the speed of motor M as set on speed-control dial 105 (as well as of the total path length from entry to exit from developer bath 92).

Where greater correlation in development times is desired, the transport arrangement of FIG. 2 can be substituted, wherein the test strip is pulled at essentially constant speed past the exposure block by added synchronous motor 50, but provision is made for storing excess exposed iilm if such initial rate of transport somewhat exceeds the subsequent rate of transport thereof through the development and monitoring chamber and for interrupting the exposing and initial transport of the test strip if such initial rate of transport greatly exceeds the subsequent rate. In such event swing arm S6 takes up the slack in the test strip until the amount of slack taken up is sufcient to lower the swing arm enough to open limit switch 63, thereby interrupting the electrical circuit to both exposure la-mp 16 and motor 50. In this embodiment the exposed test strip is pulled by synchronous motor 30 past development and monitoring block 23 and is developed in development chamber 71 therein for a time proportional to the time of development of photographic material supported by belt 90 in developer bath 92 because synchronous motor 30 is not supplied with the same electrical power supplied to synchronous motor 50 but with power from alternator G instead (see connections i, i in FIG. 8). The alternator is driven in turn by motor M, which also turns drive roll 93 to transport the subject photographic material through the developer bath. It will be understood that, to avoid a possibility of breaking the test strip, the rate of transport so provided by synchronous motor 30 when alternator G is going its fastest, corresponding to the highest setting of control dial 105 for motor M, will not exceed the rate of transport provided 'by synchronous :motor 50. A system of this type, wherein the .monitored activity level of the developer is so related to the development time of lm being processed, is especially useful in certain types of photographic work, as will be apparent to persons skilled in the art.

Accordingly, this invention provides greatly improved apparatus and methods for sampling photographic developer so as to monitor the activity thereof, for monitoring such activity so as to determine changes therein and the desirability of adding developer replenisher to compensate therefor, for adding such replenisher to compensate for such changes, particularly in accordance with sensed rate of depletion therein without exceeding an acceptable preselected plateau of activity.

Although certain embodiments have been illustrated and described by way of example, modifications may be made therein, as by adding, combining, or subdividing parts or steps, while retaining some or all of the advantages and benefits of the invention. For example, in the embodiment illustrated in FIG. 1 exposure block 13 may be combined with development and monitoring block 23 into a single block, with corresponding reduction in the number of springs and pressure pads, if desired. Individual pressure pads may be used in place of combined pad 24 in any instance, and a coil spring may be used in place of a leaf spring, of course, or other biasing means may be substituted, as may other types of pads. Other modifications may be suggested to persons ordinarily skilled in the art, in the light of the present disclosure. The invention itself is deiined in the following claims.

What is claimed is:

1. In development of photographic material in a bath of developer wherein developer activity is subject to depletion with use and a photosensitive test strip is exposed concurrently therewith, an improved developer replenishing process, comprising extracting successive samples of developer from the bath, developing the exposed test strip with the samples of developer, sensing optical density of successive portions of the developed strip, comparing the density of the last sensed portion with the density of the last previously sensed portion, and adding developer replenisher from a source thereof to the developer bath only if the density of the last sensed portion is less than the density of the last previously sensed portion.

2. Developer replenishing process according to claim 1, wherein the test strip is transported continuously at a xed rate through an exposure zone in which it is so exposed and a subsequent developing zone in which it is so developed.

3. Developer replenishing process according to claim 1, wherein the test strip is transported discontinuously, but at a fixed rate of transport during the transporting thereof, through an exposure zone in which it is so exposed, and subsequently transporting it through a development zone at a rate of transport inversely proporitoned to the time of development of the subject photographic material.

4. Developer replenishing process according to claim 1, wherein the amount of added developer replenisher is proportioned to rate of decrease in optical density from the last previously sensed portion of the test strip to the last sensed portion .of the test strip.

5. Developer replenishing process according to claim 4, wherein the developer replenisher is added periodically in amounts so proportioned.

6. In developer replenishment for maintaining activity of a bath of photographic developer subject to depletion in activity with use, wherein a test strip is developed with some of such developer, the optical density of the developed test strip is sensed, and developer replenisher is added to the bath in accordance therewith, the improvement comprising comparing the density of successively developed portions of the test strip and controlling the addition of developer replenisher in accordance with the results of such comparison by proportioning addition of replenisher to the rate of decrease in density of successively compared portions of the test strip.

A7. Developer replenishing process according to claim 6, wherein the developer replenisher is added at timed intervals and the rate of decrease is determined with respect to the last timed interval.

8. Developer replenishing process according to claim 6, wherein the amount of developer replenisher added is in excess of the amount required to compensate for the decrease.

9. Developer replenishing process according to claim 8, wherein the addition of developer replenisher is discontinued when and so long as the photosensed optical density indicates an acceptable preselected level of activity.

10. In apparatus for developer replenishment including means for exposing a photosensitive test strip, means for developing such exposed test strip in developer from a bath thereof in which photographic material is developed, and means for sensing optical density of successive portions of the test strip; improved means for controlling addition of developer replenisher from a source thereof to the bath, comprising means for comparing the sensed density of a current portion and of a previous portion of the test strip, and means for adding replenisher in accordance with the results of such comparison, wherein the means for sensing optical density of the test strip includes an electrical bridge circuit, and the control means comprises an electrical switching circuit having first and second states with respect to conduction therein, timing means for converting from the first to the second of the states of the switching circuit and thereby periodically checking the sensed optical density, switch means responsive to the conduction states of the switching circuit and having a first position precluding addition of replenisher and a second position permitting addition of replenisher and corresponding respectively to the first and second states of the switching circuit, electrical charge storage means interposed between the bridge circuit output and the switching circuit for interonneting them only in the second switch position and effective when so interconnected to determine the duration of the second state of the switching circuit and thus of the second position of the switch means.

11. In apparatus for developer replenishment including means for exposing a photosensitive test strip, means for developing such exposed test strip in developer from a bath thereof in which photographic material is developed, and means for sensing optical density of successive portions ofthe test strip; improved means for controlling addition of developer replenisher from a source thereof to the bath, comprising means for comparing the sensed density of a current portion and of a previous portion of the test strip, and means for adding replenisher in accordance with the results of such comparison, wherein the control means includes means for precluding addition of developer replenisher whenever the sensed density of the current portion of the test strip is indicative of a preselected plateau of acceptable developer activity level.

12. Apparatus for developer replenishment according to claim 11, wherein the ymeans for sensing optical density of the test strip includes an electrical bridge circuit, and the control means includes an electrical switching circuit having rst and second states with respect to conduction therein, the first state being induced by bridge output oi at least a given value indicative of sensed density corresponding to the plateau of acceptable developer density and the second state being induced by bridge output of less than that given value, switch means responsive to the conduction states of the switching circuit and having a first position precluding addition of replenisher and a second position permitting addition of replenisher and corresponding respectively to the first and second states of the switching circuit.

13. Apparatus for controlling addition of developer replenisher to a bath of photographic developer subject to depletion in activity'with use, comprising means for transporting a photosensitive test strip past an exposure location, then past a developing location, and finally past a density-monitoring location; means for extracting developer from the bath, forwarding it to the developing lo cation, and returning it to the bath; densitometric sensing means at the monitoring location, including an electrical resistor device whose electrical resistance varies in accordance with the intensity of light incident thereon; electrical comparison means including an electrical bridge circuit having that resistor device interconnected thereinto, electrical control means responsive to the bridge circuit output and electrically operated valve means for adding developer replenisher to the bath in accordance with operation of the control means; the control means comprising first and second switch lmeans having first and second positions each and both being interconnected to the electrically operated valve means to actuate such valve means when the switch means are in their respective second positions, rst and second control circuits for the respective first and second switch means, each of the control circuits having rst and second states with respect to conduction therein actuating the respective switch means to their respective first and second positions; the first control circuit including timing means for actuating its switch means periodically for the rst to the second position, electrical charge storage means interconnected to the bridge output in the second position only and retentive of a charge indicative of any decrease in bridge output corresponding to current sensed optical density as compared with the density sensed at the last previous time when the switch means was in the second position, the duration of the second state of the control circuit being proportioned to such charge; and the second control circuit being interconnected continuously to the bridge output and responsive thereto, such output being effective to maintain the circuit in the first state whenever the bridge output is at least a given value indicative of current sensed density corresponding to a plateau of acceptable developer activity and in the second state whenever the bridge output is less than that given value.

14. Apparatus for developer replenishment according to claim 15, wherein the valve means is preadjustable for rate of ow of developer replenisher such that the amount of replenisher passing therethrough during a period of actuation of the valve is in excess of the amount that would be required to compensate for the sensed decrease in optical density.

References Cited UNITED STATES PATENTS 1,895,760 l/1933 Hunt 95-89 3,354,802 11/1967 Doucette et al 355-10 JOHN M. HORAN, Primary Examiner K. C. HUTCHISON, Assistant Examiner U.S. Cl. X.R. 95-94 R Pil-1050 UNITED STATES PATENT OFFICE 569 CERTIFICATE 0F CORRECTION Patent No. 3623418 Dated 30 November 1971 Inventor(s) Clarence S- OSt It :ls certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as show-n below:

Column 3, line l, delete the comma after "shows";

Column 3, line 44, "thereform" should read therefrom;

Column 4, line 57, the semi-colon should be a comma;

Column 4, line 6l, "colsed" should read closed;

Column 5, line 34, the word "it" should be inserted after "Thus,"

Column 7, line 72, "proporitoned" should read proportioned;

Column 8 line 54, "interocceting" should read -interconnecting;

Column 9, line 28 insert a comma after "put";

Column l0, line 5, "for" should read from;

Column lO, line 2l, "l5" should read --l3.

Signed and sealed this M th day of July i 9,72.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. RO BERT QOTTSCHALK At testing Officer' Commissioner of Patents 

